The present invention relates to an image processing system wherein an image obtained by an image pickup apparatus is transmitted to and processed by an image processing apparatus. In particular, the present invention pertains to an appropriate image processing system for reducing the number of signal lines required for a connection between an image pickup apparatus and an image processing apparatus, as well as for suppressing the deterioration of an image quality, and an image pickup apparatus and an image processing apparatus that constitute this image processing system.
In an image processing system wherein an image obtained by a camera (an image pickup apparatus) is transmitted to an image processing system, the camera is connected to this image processing apparatus by signal lines so that the camera may be located at a distance from the image processing apparatus. An image processing system disclosed in Japanese Patent Publication No. Hei. 11-78692 respectively provides for the mounting of multiple cameras on the front, the rear, the left and the right side of a vehicle, and for a single image processing apparatus to be employed that fetches and synthesizes the images obtained by these cameras. For this conventional image processing system, the transmission to the image processing system of video data obtained by the cameras is performed using an arbitrary transmission method, such as RGB or YUV, or Y/C separation video or composite video.
When all video data acquired by an image pickup element, such as a CCD used for a digital camera, are to be transmitted to an image processing system, the video data are converted into RGB signals or YUV signals by the camera and the resultant signals are output to the image processing apparatus. In this case, since video data for each color element are output by the camera to the image processing apparatus, a total of three transmission paths (signal lines) are required.
To effect a reduction in the number of required signal lines, methods such as Y/C separation video and composite video are available. With the first method, two paths are required for the transmission of data, while with the second method, one path is required. However, since when these methods are employed, the amount of data that is transmitted for an image is reduced from that which is acquired by an image pickup element, and the quality of the image, when it is subsequently reproduced, is deteriorated.
When transmission along two paths is to be preformed without a reduction in the amount of data, a point sequential system for alternately transmitting a color difference U/V signal for each pixel is employed. According to the point sequential system, since a color mixture occurs when the U/V separation timing is shifted at the reception time, accurate timing management is indispensable. Therefore, when the point sequential system is employed for a monitoring system, or a vehicle-mounted system, for transmitting data a long distance of several meters to several tens of meters, deterioration of the signal occurs and using the system is difficult.
Three transmission paths are required for the transmission of a high quality video signal. However, this involves an increase in the number of lines, and the transmission at a long distance is indispensable for the application to the monitoring system, so that the costs for laying long cables would be increased. Further, as is disclosed in Japanese Patent Publication No. 11-78692, for an image processing system for which multiple cameras are mounted on a vehicle, because the available mounting space is severely limited, it is imperative that the number of signal lines and the size of the apparatus be reduced. This is especially true when multiple cameras are employed for a monitoring or a vehicle mounted system, since then, either multiple scenes are alternately displayed or multiple images are synthesized and the resulting image is displayed or recorded. As a result, therefore, when the number of cameras is increased, the accompanying increase in the number of video signal transmission paths and in the size of the processing circuit constitute a formidable problem.
Specifically, when for a conventional image processing system all video data acquired by cameras are to be transmitted to an image processing apparatus, the number of signal transmission lines that are required is increased, as are the number of circuits in the image pickup apparatus and the size of the video signal input/output section of the image processing apparatus. This problem becomes evermore apparent as the number of mounted cameras is increased.